Printer Friendly Forum Posts - relays, handsfree liftgate

OK, I'll try to make this short, but I'm not sure how well I'll do;) I'm not sure if you guys have seen the handsfree liftgate on the new Ford Escape, but briefly you walk up to the car and even if your hands are full you can stick your foot under the rear bumper and (as long as you have the keyfob in your pocket) it will unlock the doors and open the liftgate for you.

I'm attempting to replicate this on my highlander. It already has a keyless entry system that will unlock the doors if I have the keyfob in my pocket and I press the hatch release button on the hatch. It also has a motorized hatch and a hatch open button on the dash that will only operate when the doors are unlocked and the car is in park.

I'll need to figure out something to trigger this... possibly just a button under the car to kick which should be cheap and easy, but isn't quite as cool as a motion sensor. I may consider doing a motion sensor too.

I've already run a wire up to the dash and connected it to the 'hatch open' button there. The button needs to be held for at least one second to trigger (presumably to prevent the hatch from opening if you accidentally hit the button). So, if I connect the wire I ran to ground and hold it for at least one second the hatch will open.

I've also run a wire up to the roof of the car and tied it in with the hatch release button on the outside of the hatch. If I connect this wire to ground (and the keyfob is near the car) the doors will unlock.

So, my plan is to trigger this with either a double pole momentary switch, or some sort of a motion detector that will trigger a double pole relay. One pole on the relay or switch will connect the unlock circuit to ground so the doors unlock if the keyfob is near by.

Once the second pole is connected, then released it will need to trigger something that will connect the 'open hatch' circuit to ground and hold it there for one second. It needs to trigger *after* the second pole has been released because if the unlock circuit and open hatch circuit are connected to ground at the same time the doors unlock, but the hatch never opens.

So, if you're still with me after all that, this second bit is the part I need help with. I'm thinking I can probably do this with a couple of relays, but I'm not quite sure how to connect them. Again, what I need is something that will trigger only after the button (or relay) has been pressed *and then released*. Once that happens I need to connect a wire to ground for 1 full second (slightly longer is fine, but it can't be any shorter), then release it.

I've looked through the relay diagrams here and I can't find anything that will fit my needs, so I'm hoping someone can come up with something for me here.

I'm also looking for ideas on how to trigger the whole thing too. If you know of any large waterproof buttons that could be mounted under the car and easily kicked, or even a waterproof motion sensor that could be mounted under the car, please let me know.

Thanks much,
Brett